The health of chrysotile asbestos mine and mill workers of Quebec

Our plain-English summary of The health of chrysotile asbestos mine and mill workers of Quebec, by J.C. McDonald, M.R. Becklake, G.W. Gibbs, et al (Archives of Environmental Health, 1974).

The study

• Authors: J.C. McDonald, M.R. Becklake, G.W. Gibbs, A.D. McDonald, C.E. Rossiter
• Journal: Archives of Environmental Health
• Published: 1974;28(2):61-8
• Cited by: 96 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001281).

In plain English

The authors combined their studies, begun in 1966, of Quebec chrysotile mine and mill workers. Records identified some 28,000 workers, mostly men. Exposure was measured in million particles per cubic foot times years (mpcf-yr). In a mortality cohort of 11,572 people born 1891 to 1920, 3,270 had died by December 1969. Of 134 respiratory cancer deaths in men, five were pleural mesotheliomas; none were peritoneal. Expected deaths numbered 139 by Quebec rates, or about 93 by mining-region rates. Each case was compared with four random controls alive at his death and born the same year. The relative risk of death from respiratory cancer was 5.0 at 800+ mpcf-yr, against under 10 mpcf-yr. In 1,015 workers tested, forced vital capacity fell about 18% in the highest dust group. The authors concluded that excess mortality was virtually confined to men with at least 400 mpcf-yr. Because their particle counts could not be reliably converted to fiber counts, they concluded it was unwise to stop using particle counts for control in this industry until new epidemiological evidence based on fiber counts was assembled.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Overview bringing together the authors' own studies: a mortality cohort (with a case-control analysis of respiratory cancer deaths), chest X-ray surveys, lung function tests and respiratory symptom questionnaires
• Who was studied: Some 28,000 employees, mostly men, identified from records of the Quebec chrysotile mining and milling industry since 1878. The mortality cohort was 11,572 persons born 1891 to 1920, of whom 87.5% were traced by the end of December 1969. Lung function and symptom surveys covered 1,015 current employees in 1967 and 1968.
• Exposure: Chrysotile asbestos dust in mining and milling. Exposure was measured as a total dust index from midget impinger particle counts, in million particles per cubic foot multiplied by years at that level (mpcf-years).
• Main results:
  • Of 134 respiratory cancer deaths in men, five were from pleural mesothelioma. These five showed no clear relationship with dust exposure, and there were no peritoneal mesotheliomas.
  • The expected number of respiratory cancer deaths in the cohort was 139 based on Quebec death rates, or about 93 based on estimated mining-region rates. The authors suggested that respiratory cancer mortality in the industry as a whole was at most 50% above expectation and probably about 25%.
  • In the case-control analysis, each of the 134 men who died of respiratory cancer was compared with four controls chosen at random from persons alive at the time of the case's death and born in the same year (536 controls in all). The relative risk of death from respiratory cancer was 5.0 in the 800+ mpcf-yr group (19 cases, 22 controls), compared with 1.0 in the under 10 mpcf-yr group.
  • Excess deaths related to exposure were probably no more than 2% of the 3,270 deaths in the cohort study, and were virtually confined to men with exposure of at least 400 mpcf-yr.
  • Pleural calcification of grade 1 or more was found in 0.4% of workers at Asbestos and 5.2% at Thetford Mines.
  • Irregular small opacities of category 2 and pleural thickening of grade 2 occurred in 1.0% and 0.7%, respectively, of the entire working population.
  • Among men in the lung function survey, forced vital capacity fell by about 18% in the highest dust group, and FEV1 fell rather less.
  • Breathlessness on exercise was unaffected by smoking but increased steadily with dust exposure.
  • Calcified pleural plaques were not related to mortality: there were 60 deaths in persons with pleural plaques, against 59 expected.
• The authors' conclusion: The authors concluded that, considering all aspects of disease, a 1% risk was reached in their third dust exposure category (100 to 200 mpcf-yr). They put a reasonable standard between 2 to 4 million particles per cubic foot over a 50-year working life. Because they could not confidently express their results in fiber counts, they also concluded that it appeared unwise to discontinue particle counts for control in this industry until new epidemiological evidence based on fiber counts had been assembled.
• Limitations the authors state:
  • Side-by-side particle and fiber measurements correlated too poorly to justify any single conversion factor, so the results could not be expressed in fiber counts.
  • In the earlier mortality analysis, length of exposure may have been related to length of survival, which could obscure differences between exposure groups.
  • Earlier company records tended to be incomplete or missing, and some had been destroyed.
  • Smoking habits were originally recorded only for employees in the lung function survey, not for the mortality cohort.
  • Duration and concentration of exposure could not easily be separated, so the authors cautioned against applying the results to widely different exposure patterns.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile.

Related studies

• Mortality in the chrysotile asbestos mines and mills of Quebec — J.C. McDonald, A.D. McDonald, et al. (1971)
• Lung function profiles in the chrysotile asbestos mines and mills of Quebec — M.R. Becklake, G. Fournier-Massey, et al. (1976)
• Rheumatic complaints and pulmonary response to chrysotile dust inhalation in the mines and mills of Quebec — F.M. White, J. Swift, et al. (1974)
• Non-malignant consequences of decreasing asbestos exposure in the Brazil chrysotile mines and mills — E. Bagatin, J.A. Neder, et al. (2005)
• Late progression of radiographic changes in Canari chrysotile mine and mill exworkers — J.R. Viallat, C. Boutin, et al. (1983)
• Exploratory sampling of asbestos in residences near Thetford Mines: the public health threat in Quebec — M. Marier, W. Charney, et al. (2007)

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